The present invention relates to a method and apparatus for cleaning or separating lighter unwanted matter from heavier granular material. The invention is particularly applicable to cleaning the granular material during transfer thereof from one location to another.
Granular material to be used in forming a solid end product can often carry unwanted matter detrimental to the end product. A specific example is ground plastic used as a plastic supply for molding operations and the like. The plastic, in granulated form, may be ground from a larger block of xe2x80x9cparentxe2x80x9d material. This parent material may be either virgin or recycled material. The granular plastic may also be re-pelletized material.
When working from a solid block of plastic during the grinding or regrinding operation, varying amounts of parent material dusts are generated within and carried by the granulated plastic. Depending on the size of the dust particles, they can create problems in the molded or otherwise produced, end product.
In the case of re-pelletized material this material tends to pick-up unwanted matter which settles on the material during storage thereof.
In the examples given, due to the heat process required, the dusts and other unwanted matter tend to carbonize rather than melt. As such they turn up as impurities in the final product. Accordingly it is important to clean the unwanted matter from the granular plastic material before using it in the product formation process. A particularly suitable time for doing this is when the granular material is being transferred from one location to another.
The present invention provides a method and apparatus for separating or cleaning unwanted fine matter from heavier or more dense granular material. Preferably the flow of the material occurs vertically through a containment and separation housing while the material is being transferred from one location to another e.g. from a supply source to a storage site for the material or from a storage site to a use site for the material.
According to the method of the invention, flow of the material is produced, under vacuum, firstly through alternating expansion and contraction passages and then against impact surfaces to cause multiple redirections of the material. This causes a fallout of the heavier material particles while the lighter unwanted matter is carried away by the vacuum.